Laser system and electronic device manufacturing method

Abstract

A laser system according to one aspect of the present disclosure includes a wavelength-variable first solid-state laser device configured to output a first pulse laser beam; a wavelength conversion system including a first nonlinear crystal configured to wavelength-convert the first pulse laser beam and a first rotation stage configured to change a first incident angle of the first pulse laser beam on the first nonlinear crystal; an excimer amplifier configured to amplify a pulse laser beam wavelength-converted by the wavelength conversion system; and a control unit configured to receive, from an external device, data of a target center wavelength of an excimer laser beam output from the excimer amplifier, control a wavelength of the first pulse laser beam in accordance with the instructed target center wavelength, and control the first incident angle on the first nonlinear crystal in accordance with an average value of the target center wavelength.

What is claimed is: 
     
       1. A laser system comprising:
 a wavelength-variable first solid-state laser device configured to output a first pulse laser beam; 
 a wavelength conversion system including a first nonlinear crystal configured to wavelength-convert the first pulse laser beam output from the first solid-state laser device and a first rotation stage configured to change a first incident angle of the first pulse laser beam on the first nonlinear crystal; 
 an excimer amplifier configured to amplify a pulse laser beam wavelength-converted by the wavelength conversion system; and 
 a control unit configured to receive, from an external device, data of a target center wavelength of an excimer laser beam output from the excimer amplifier, and control the first incident angle on the first nonlinear crystal such that wavelength conversion efficiency of the first nonlinear crystal has a maximal value at a middle wavelength in a first wavelength range to which the target center wavelength belongs, 
 the first wavelength range being separated to include, as a boundary wavelength in the first wavelength range, a wavelength at which a first allowable efficiency minimum value lower than maximum conversion efficiency of the first nonlinear crystal is obtained in accordance with a characteristic of the wavelength conversion efficiency of the first nonlinear crystal changing depending on the first incident angle and the wavelength, and the wavelength conversion efficiency of the first nonlinear crystal being determined to be equal to or higher than the first allowable efficiency minimum value at a specific first incident angle for each first wavelength range. 
 
     
     
       2. The laser system according to  claim 1 , wherein
 the first allowable efficiency minimum value is 80% or higher of the maximum conversion efficiency of the first nonlinear crystal. 
 
     
     
       3. The laser system according to  claim 1 , wherein
 the control unit controls the first solid-state laser device such that pulse energy of the first pulse laser beam output from the first solid-state laser device has a predetermined constant value, and 
 when pulse energy of the excimer laser beam output from the excimer amplifier with wavelength conversion efficiency of the wavelength conversion system being maximum is Emax, an allowable energy decrease rate allowed for Emax is Ear, a minimum energy value allowed for the pulse energy of the excimer laser beam is Emin, pulse energy of the pulse laser beam after wavelength conversion output from the wavelength conversion system with the wavelength conversion efficiency of the wavelength conversion system being maximum is Esmax, a lower limit of a range of variation of the pulse energy of the pulse laser beam after wavelength conversion output from the wavelength conversion system due to a change in the wavelength of the first pulse laser beam is Esmin, and a rate of change in the pulse energy of the pulse laser beam after wavelength conversion output from the wavelength conversion system is Esr, the following expressions are satisfied:
     Ear =( E max− E min)/ E max
 
     Esr =( Es max− Es min)/ Es max
 
     Ear/Esr≤ 0.01. 
 
 
     
     
       4. The laser system according to  claim 1 , wherein
 the control unit controls the first solid-state laser device such that the pulse energy of the first pulse laser beam output from the first solid-state laser device has a predetermined constant value, calculates a predicted value of the pulse energy of the pulse laser beam after wavelength conversion output from the wavelength conversion system in accordance with the pulse energy of the first pulse laser beam and the wavelength conversion efficiency of the wavelength conversion system, and controls a charging voltage of the excimer amplifier in accordance with the predicted value and target pulse energy of the excimer laser beam output from the excimer amplifier. 
 
     
     
       5. The laser system according to  claim 1 , wherein
 the control unit controls the pulse energy of the first pulse laser beam output from the first solid-state laser device such that the pulse energy of the pulse laser beam after wavelength conversion output from the wavelength conversion system has a predetermined target value. 
 
     
     
       6. The laser system according to  claim 1 , wherein
 the wavelength conversion system includes a second nonlinear crystal that the pulse laser beam wavelength-converted by the first nonlinear crystal enters, and a second rotation stage configured to change a second incident angle, on the second nonlinear crystal, of the pulse laser beam wavelength-converted by the first nonlinear crystal, 
 the control unit controls the second incident angle on the second nonlinear crystal such that wavelength conversion efficiency of the second nonlinear crystal has a maximal value at a middle wavelength in a second wavelength range to which the target center wavelength instructed by the external device belongs, 
 the second wavelength range is separated to include, as a boundary wavelength in the second wavelength range, a wavelength at which a second allowable efficiency minimum value lower than maximum conversion efficiency of the second nonlinear crystal is obtained in accordance with a characteristic of the wavelength conversion efficiency of the second nonlinear crystal changing depending on the second incident angle and the target center wavelength, and the wavelength conversion efficiency of the second nonlinear crystal is determined to be equal to or higher than the second allowable efficiency minimum value at a specific second incident angle for each second wavelength range. 
 
     
     
       7. The laser system according to  claim 1 , further comprising a second solid-state laser device configured to output a second pulse laser beam having a wavelength different from the wavelength of the first pulse laser beam, wherein
 the first nonlinear crystal generates first sum frequency light from the first pulse laser beam and the second pulse laser beam, 
 the wavelength conversion system outputs a third pulse laser beam as the pulse laser beam after wavelength conversion from the first pulse laser beam and the second pulse laser beam, and 
 the third pulse laser beam enters the excimer amplifier.